The present invention relates to an electronic device such as an RF modulator, and more particularly to a case for housing and shielding a circuit of the electronic device.
FIGS. 1 and 2 of the accompanying drawings illustrate a conventional case for electronic devices. FIG. 1 shows the case in perspective with a cover removed and a bottom facing up, and FIG. 2 shows the case with the cover attached in a side elevation.
The illustrated case is used for an RF modulator having an antenna booster mixer or an RF modulator having an antenna booster switch.
Designated by the reference character 1 is a metal frame forming side plates of the case. A circuit board 2 is secured to the metal frame 1 near the bottom thereof (upper edge, as shown). The circuit board 2 supports an antenna circuit on a lefthand half portion thereof (indicated by A) and a circuit constituting an RF modulator on a righthand half portion thereof (indicated by B). To shield the circuits from each other, the interior of the frame 1 is partitioned by a shield plate 3 which is formed by bending a portion of the frame 1. The shield plate 3 has two divided end portions extending respectively through holes 2a defined in the circuit board 2 into a bottom opening (an upper opening as shown) in the frame 1. The two end portions of the shield plate 3 have distal ends bent at a right angle to provide contact legs 3a. A metal cover 4 is mounted in the upper opening in the frame 1 and has an inner surface in contact with the contact legs 3a to keep the shield plate 3 and the cover 4 at the same potential (see FIG. 2). A ground pattern of the antenna circuit (on side A) on the circuit board 2 is connected by solder bodies 5a to the shield plate 3, and a ground pattern of the RF modulator (on side B) is connected by solder bodies 5b to the shield plate 3. As illustrated in FIG. 2, another cover 6 is mounted in a lower (FIG. 1) opening of the frame 1. Two input and output connectors 7 are mounted on a lower side of the frame for connection to an antenna, and an output connector 8 is mounted on a lateral side of the frame 1 for connection to a tuner.
The above conventional case for electronic devices has had the following problems:
(1) The holes 2a defined in the circuit board 2 have to have a certain size so as to allow the contact legs 3a to pass therethrough. Since there are gaps formed between edges defining the holes 2a and the shield plate 3, the solder bodies 5a are required to be formed as bridges as shown in FIG. 2, a soldering process which is quite difficult to accomplish.
(2) To facilitate the soldering operation for forming the solder bodies 5a as bridges, it is necessary to form the ground pattern on the circuit board 2 close to the edges of the holes 2a. Therefore, difficulty has been encountered in forming the pattern on the circuit board 2.
(3) When applying the solder bodies 5b to the RF modulator circuit, the solder tends to flow onto the contact legs 3a. The solder on the contact legs 3a makes the upper surface thereof irregular rather than smooth, imparing contact between the contact legs 3a and the inner surface of the cover 4. Accordingly, the shield capability is reduced, which renders the antenna terminal voltage unstable and produces cover noise.